The second boom in Death Valley was tourism, started in the 1920s by Herman Eichbaum. After several failures in getting a toll road approved from Lida, Nevada or over Towne Pass, he scaled back plans to include only the part of the latter route between southeast of Darwin and his resort at Stovepipe Wells. The new Eichbaum Toll Road was certified complete on May 4, 1926, and toll rates were set: $2 per motor vehicle and 50¢ per person. In 1933, the state legislature added many roads to the state highway system, including a new (unsigned) Route 127, connecting Tipton with Baker via Lone Pine and Death Valley Junction.[10][11] The Death Valley National Monument was created on February 11, 1933, and in December 1934 the Division of Highways paid $25,000 for the 30.35-mile (48.84 km) road, giving the 17 miles (27 km) east of the park boundary at the pass to the National Park Service.[12] The state Division of Highways and National Park Service soon paved the route from Lone Pine (on US 395) through Towne Pass and Death Valley to Baker (on US 91).[13] The work was completed in October 1937, including the 17.5-mile (18 km) Darwin cutoff that bypassed Darwin and the old toll road west of Panamint Springs.[14] The National Park Service, using Civilian Conservation Corps labor, maintained the road through the park until August 1942, when an 11-mile (18 km) stretch east of the valley was washed out by a storm. At that time, maintenance was given back to the state, which rebuilt the destroyed segment.[3]

When the state sign route system was created in 1934, Sign Route 190 was assigned to the portion of Route 127 west of Death Valley Junction, while the remainder to Baker became part of Sign Route 127.[15] However, the highway was not continuous, with the roadway from Tipton (which had been built by Tulare County[16]) ending at Quaking Aspen (east of Camp Nelson) and that from Death Valley ending southwest of Lone Pine.[17] In 1923, Tulare County businessmen had begun to push for a new trans-Sierra highway connecting Porterville with Lone Pine,[18] but were set back by a lack of state aid, as the road was not a state highway.[19] The first piece, which would turn out to be the only one built, opened in early July 1931 to Quaking Aspen (and became a state highway in 1933).[20] Grading of the 15-mile (24 km) Western Divide Highway, a county road that was supposed to continue south to State Route 155 at Greenhorn Summit,[21] was completed from Quaking Aspen south to near Johnsondale in July 1962.[22] A new road from Johnsondale across Sherman Pass, maintained by the U.S. Forest Service and Tulare and Inyo Counties (the latter as County Route J41), was completed in 1976, allowing traffic on the western segment of SR 190 to reach US 395, though via a longer route than the proposed SR 190.[23]

In March 1959, Tulare County approved a change in location of the proposed highway to Olancha Pass[24] (Haiwee Pass, just to the south, was soon considered for a possible alternate location[25]), and the legislature moved the main line of Route 127 south to that location, crossing US 395 at Olancha, later that year. The old route from southeast of Keeler to Lone Pine remained as a branch,[26] and was still signed as SR 190.[27] Also in 1959, the original routing from Lone Pine through Death Valley to Baker was added to the proposed California Freeway and Expressway System, though no parts have been upgraded as such.[28] The east–west piece between Tipton and Death Valley Junction legislatively received the State Route 190 designation in the 1964 renumbering, and the north–south part became State Route 127, which it had been signed as; the branch to Lone Pine became a new State Route 136.[29] By the mid-1970s, the environmental movement had essentially killed the planned connection,[23] and the designation of the Golden Trout Wilderness in 1978 and South Sierra Wilderness in 1984 were the final blow, though Caltrans still has an officially adopted alignment designated over Haiwee Pass.[3]

Except where prefixed with a letter, postmiles were measured on the road as it was in 1964, based on the alignment that existed at the time, and do not necessarily reflect current mileage. R reflects a realignment in the route since then, M indicates a second realignment, L refers an overlap due to a correction or change, and T indicates postmiles classified as temporary (for a full list of prefixes, see the list of postmile definitions).[1] Segments that remain unconstructed or have been relinquished to local control may be omitted. The numbers reset at county lines; the start and end postmiles in each county are given in the county column.

^California State Assembly (1963). "An act...relating to routes on the state highway system". 1963 Session of the Legislature. Statutes of California. State of California. Ch. 385 p. 1185.: "Route 190 is from Route 99 near Tipton to Route 127 near Death Valley Junction via the vicinity of Porterville, Camp Nelson, Olancha, and Death Valley."